The polarized light transmittance of magnetic fluids under longitudinal magnetic field (parallels the propagation direction of the incident light) is simulated theoretically. The investigated samples are with different reduced thickness ( ) in a wide range. Theoretical simulations reveal that the sample reduced thickness has a significant influence on the polarized light transmittance. The thin and thick samples have distinctly different dependence of polarized light transmittance on magnetic field strength. Based on the reduced-thickness- and magnetic-field-dependent polarized light transmittance, several magnetic-fluid-based photonic devices are proposed and discussed. 1. Introduction Magnetic fluids as optical functional materials have attracted much attention recently. The promising prospect in optical applications and photonic devices is disclosed through versatile experimental results in the laboratory. For example, Ge et al. have experimentally realized the magnetic-field-responsive photonic crystals by magnetically induced colloidal assembly within magnetic fluids [1–3]. Zhang et al. have observed the magnetic field modulation of light transmission through binary magnetic fluid films [4]. The magnetic-field-dependent light transmittance is one of the important optical properties of magnetic fluids, which is usually employed to design some photonic devices and should be investigated in depth. This work will focus on the transmittance of polarized light passing through magnetic fluids under longitudinal magnetic field. The longitudinal magnetic field means that the magnetic field parallels the propagation direction of the incident light. For the longitudinal magnetic field configuration, the magnetic-field-dependent optical transmittance of magnetic fluids is chiefly assigned to the column/chain formation of magnetic particles along the magnetic field direction and the related geometric shadowing effect [5–8]. If the polarized light is applied for the longitudinal magnetic field configuration, Faraday rotation and geometric shadowing effect will happen simultaneously. In our previous work, we have disclosed that several parameters may influence the magnetic-field-dependent optical transmittance of magnetic fluids due to hybrid effects of Faraday rotation and geometric shadowing [9]. But only the thin samples with small values of reduced thickness ( , where is the thickness of the magnetic fluids and is the wavelength of the incident light in vacuum) have been considered in that work. In this work, the magnetic-field-dependent optical transmittance
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